Refining our Notion of What Text Really Is: The Problem of Overlapping
Hierarchies

Authors

Allen Renear, Brown University

Elli Mylonas, Harvard University

David Durand, Boston
University

Status

Draft version, January 6, 1993. A revised version of this paper is
forthcoming in 1995 in Research in Humanities Computing, Oxford
University Press, edited by Nancy Ide and Susan Hockey. An earlier
version was presented at the annual joint meeting of the Association
for Humanities Computing and the Association for Literary and
Linguistic Computing, Oxford University, April 1992.

We examine the claim that 'text is an ordered hierarchy of content
objects'; this thesis was affirmed by the authors, and others, in the
late 1980s and has been associated with certain approaches to text
processing and the encoding of literary texts. First we discuss the
nature of this claim and its connection with the history of text
processing and text encoding standardization projects such as SGML and
the Text Encoding Initiative. We then describe how the experience of
the text encoding community, as represented and codified in the TEI
Guidelines, have raised difficulties for this
thesis. Next we consider two progressively weaker versions of this
thesis formulated in response to these difficulties. Ultimately we
find that no version appears to be free from counterexample.

Although none of these formulations proves to be theoretically
sound, they are nonetheless methodologically illuminating as each
generalizes actual encoding practices, making explicit certain
assumptions that, even though they have been fundamental to the
working methodologies of most text encoding projects, have never been
explicitly articulated, let alone explained or defended. The
counterexamples to the different versions of the OHCO thesis also
arise in actual encoding projects -- so although our focus is
theoretical it is grounded in the methodology and problems of
contemporary encoding practices. The problems discussed here have
implications not only for text encoding and our understanding of the
nature of textual communication, but raise very fundamental issues in
the logic and methodology of the humanities.

It has been argued in many places and in many ways that documents
are 'hierarchies of content objects' (e.g. Coombs,
et al. 1987; DeRose, et al. 1990).[1] Text, according on this
view, is essentially composed of nesting objects such as chapters,
sections, paragraphs, extracts, lists, and so on. Those of us involved
in humanities computing are likely to connect this claim with projects
developing standards for encoding machine-readable texts. In this
context the 'OHCO thesis' has proven to be a serviceable ideology in
promoting the 'descriptive markup' approach to representing literary
texts in machine-readable form -- and, more specifically, it has
provided a congenial framework for the Text Encoding Initiative. But
before it was adduced for this purpose the view that text was a
hierarchy of content objects was implicit in early efforts to theorize
about the development of text processing and typesetting software (Goldfarb 1981, Reid
1980). In fact, versions of this view which are entirely
independent of any interest in computing applications can be discerned
in the rhetoric of the 'parts of a book' which has been prevalent in
style manuals and bibliography handbooks for some time (Renear, 1993).

Surprisingly, this thesis has undergone remarkably little
refinement, extension, or clarification over the years it has served
as the theoretical background for text processing research and text
encoding standardization. This is due in part to the fairly implicit
and heuristic role it plays in these activities. The Guidelines of the
Text Encoding Initiative exhibit a characteristically ambiguous
stance: although they seem to privilege this view and benefit from its
influence, they do not specifically invoke, explain, or defend it.

Recently practitioners of text encoding have found themselves
wrestling with some practical problems that seem to call this thesis
into question. One of these may be called the 'problem of overlapping
hierarchies' (Barnard, et
al. 1988). This problem is generally taken to be purely a
technical difficulty, the solution of which is to be found in any
particular instance by considering the practical trade-offs of
different encoding techniques. In fact, we think that the continuing
perplexity that surrounds the treatment of overlapping hierarchies is
not due to the technical issues of encoding at all, but rather to a
more fundamental deficiency in our understanding of just what we are
doing when we prepare an encoded text. The simple tenet that 'text is
a hierarchy of content objects' fails us here'. Moreover, since the
assumption of hierarchy rests primarily on its practical advantages --
and sufficiency -- for a variety of applications, rather than a
principled analysis, we do not even have adequate terminology for
describing the problems that arise.

This paper tries to take a few steps towards refining our notions
both of what text is and what we are doing when we encode a text. As a
device for raising these theoretical issues we focus primarily on the
problem of nonhierarchical relations as this problem is actually
encountered in ongoing text encoding projects.[2] We will see how an analysis of these
problems bears on the slogan that 'text is a hierarchy of content
objects'. In the process we will make explicit some of the assumptions
behind current encoding practices. These assumptions, which are not
always consistent, turn out to raise very profound issues, not only
for text encoding, but for our understanding of the nature of textual
communication and the logic and methodology of the humanities. As this
is only an attempt to begin the necessary groundwork for a theory of
text encoding, we have focused on expressing basic intuitions rather
than rigorous and exact analyses -- those will come later.

Any discussion of 'what text is' broaches topics already
well-developed in literary theory, the theory of textual criticism and
scholarly editing, and the ontology of literary works. We will not be
surveying these areas or attempting to directly relate our findings to
discussions taking place there. Our intent is only to take a small
step toward the development of a theory of 'what text is' by
generalizing from the lessons of actual encoding efforts. This is a
somewhat indirect way of proceeding to attack the general theoretical
question of the nature of text, but we suspect that there is some
benefit in a fresh perspective from an entirely new direction. Perhaps
someday the theories generated in this empirical fashion will
encounter -- either in agreement or contradiction -- the more general
a priori reasoning of literary theorists and philosophers. Before
beginning we would like to fry a red herring. Most recent criticisms
of descriptive markup and the content object approach to text have
been motivated by supposed methodological problems in recognizing the
features to be encoded -- these are the familiar and perennial
controversies surrounding the 'subjective' and 'interpretative' nature
of text encoding. Although these issues are important they are not our
issues in this essay. We are rather concerned here with the internal
coherence of the OHCO thesis itself and not with discovery procedures
for content objects. Of course it may turn out in the end that the
epistemology and metaphysics of text objects are profoundly entangled
with each other -- but that is a conclusion one should reach as the
result of argument and analysis, and not assume at the outset of an
investigation of the principles implicit in current encoding
practices.

Our provisional attitude towards this issue is simple. The process
of preparing a machine-readable text is in all essentials exactly like
the process of preparing a traditional edition. No edition can be
entirely 'theory-free', although they vary in the extent to which they
are tendentious. Similarly for text encoding: no encoded text is
strictly speaking 'theory-free', but without text encoding there is no
machine-readable text at all. It should be a commonplace that
machine-readable texts are 'subjective' and 'interpretive', but not
especially subjective or interpretative. So we endorse
Michael Sperberg-McQueen's first axiom about the markup used to
implement text encoding: Markup reflects a theory of
text (Sperberg-McQueen 1991). In fact,
what follows can be considered to a large extent an extended
meditation on this axiom.[3]

OHCO-1 gives the ontological question 'what is text?' an equally
ontological answer: text is an ordered hierarchy of content objects
(DeRose, et al. 1990). The claim here is that in
some relevant sense of 'book', 'text', or 'document' (perhaps qua
intellectual objects) such things are 'ordered hierarchies of
content objects'. A book for instance is a sequence of chapters, each
of which is a sequence of major sections, each of which in turn is a
sequence of subsections. Within the lowest level subsections are
objects like paragraphs, sentences, prose quotations, verse
quotations, equations, proofs, theorems, and so on. Many of these
objects can be decomposed further. This structure is hierarchical
because these objects 'nest' inside one another like Chinese boxes. It
is ordered because there is a linear relationship to objects -- for
any two objects within a book one object comes before the other.[4] Finally, we call these
objects content objects because they organize text into natural units
that are, in some sense, based on meaning and communicative
intentions.[5]

The OHCO view of text can be contrasted with other models of text
generalized from the software, practices, or methodologies that embody
them: bitmaps (raster images), characters and formatting commands
(procedural markup), glyphs and white space, character transcripts
(the so-called 'ASCII' or 'text only' form of a document), and layout
hierarchies.[6]

In both text processing and textbase development the superiority of
the OHCO approach over these other models can be shown easily -- it is
by far the simplest and most functional way to create, modify, and
format texts; it is required to support effectively text retrieval,
browsing, analysis, and other sorts of special processing; and texts
represented according to this model are much more easily shared among
different software applications and computing systems. The motivation
for the view that texts are hierarchies of content objects lay
initially in reflecting on these practical benefits of treating texts
as if they were ordered hierarchies of content objects.

The early positive arguments for text being a hierarchy of content
objects were advanced largely to promote a particular approach to text
processing and text encoding and to discourage the competing
alternatives. The partisans of content-oriented text processing and
descriptive markup claimed that treating texts as if they were ordered
hierarchies of content objects had many practical benefits, while
alternative representational practices resulted in various
inefficiencies and inadequacies. It was a short step from noting the
practical advantages of treating texts as if they were OCHOs to
explaining those advantages by the hypothesis that texts are
OHCOs. But once this hypothesis had been motivated by its practical
advantages corroborating arguments of various kinds can be found.

Arguments that text is a structure of content objects are grouped
here into three broad categories: pragmatic, empirical, and
theoretical. This overview is designed only to briefly review the
sorts of aguments that have been made; it is neither an endorsement
nor a complete presentation of them. Of most interest here are the
structure of the arguments and the assumptions underlying them.

Pragmatic arguments are based on the practical advantages of the
OHCO model. They originate with the designers of text processing
software but have a broad appeal to anyone working with texts on the
computer. These arguments begin, as described above, with the
observation that there are many practical advantages to modeling a
text as an OHCO rather than using one of the alternative models. Text
modeled as OHCOs are easier to create, modify, print according to
varying specifications, transfer from one application to another, and
so on. Many of the analytic procedures or specialized processing one
might want to do with a text are not even possible unless the OHCO
structure is represented. These phenomena of the comparative
efficiency and functionality of texts represented as OHCOs are best
explained, according to this argument, by the hypothesis that texts
are ordered hierarchies of content objects.

The argument has this form: If you treat texts as ordered
hierarchies of content objects many practical advantages follow, but
not otherwise. Therefore texts are ordered hierarchies of content
objects.

Obviously only those theoretically inclined will explicitly draw
the ontological conclusion -- text is an ordered hierarchy of content
objects -- rather than the practical one: treat a text as (or model a
text as) an ordered hierarchy of content objects. In fact, one can
even argue for the usefulness of descriptive markup without claiming
that one is treating texts as OHCOs, and many early promoters of
descriptive markup did just that -- the issue of what they treated
text as just did not arise. But it is difficult to explain the
effectiveness of descriptive markup without saying, for instance, that
one is identifying the relevant parts of a text or its stable salient
features. If one then reflects on these explanations it is hard to to
deny that one is representing the text as a certain kind of thing
which consists of parts (objects) arranged in a particular way, to
form a certain kind of structure: an ordered hierarchy of content
objects.

Closely related to the pragmatic arguments is a class of arguments
that might be called empirical. These begin by observing that content
objects and their relations figure very prominently in our talk about
texts, and specifically in our descriptions, explanations, theories,
hypotheses, and generalizations about texts. For instance, our
theories and conjectures about literature make extensive use of terms
for chapters, titles, sections, paragraphs, sentences, footnotes,
stanzas, lines, acts, scenes, speeches, etc. These have prominent
explanatory roles in our talk about texts and in our theorizing about
texts and related subjects such as authorship, literary history,
criticism, poetics, and so on. If we follow the recommendations of
many philosophers of science and resolve ontological questions by
looking to the nominal phrases in our theoretical assertions, then we
will conclude that such things -- chapters, verses, lines, etc. -- are
indeed the stuff of which literature is made.[7]

The empirical argument has this form: Content objects and their
relations are the principal theoretical entities referred to by our
theories, explanations, and descriptions regarding texts.
Therefore texts are relations of content objects.

The arguments in this category are generally the least convincing,
perhaps because they quite explicitly reveal the abstract and
philosophical nature of the project proposed by the question: 'What is
text?'. Nevertheless they are surprisingly common, in some form or
other, when text encoders attempt to resolve hard problems in a
principled way, or to justify their methodological resolutions.

The most important theoretical argument is a classic argument from
variation of the sort used to distinguish essential from accidental
properties in scholastic metaphysics, or, in a more contemporary
philosophical idiom, to establish 'identity conditions' for
objects. It notes that if a layout feature 'of a text' (such as
leading or typeface) changes, the text 'itself' still remains
essentially the same, but if the number or structure of the text's
content objects changes -- say the number of chapters varies or one
paragraph is replaced by another -- then we no longer, strictly
speaking, have 'the same text'. You and I can both be reading the
'same text', say Moby-Dick, even though mine is in Times
and yours in Palatino, or even though mine is in 10 point type and
yours in 12 point type -- so that mine has more typographical lines,
pages, and line end hyphens. On the other hand if my copy has fewer or
different paragraphs than yours, or has its sentences in an entirely
different order, then that seems to decisively argue that we are not
reading 'the same text'.[8]

The argument goes like this: x and y are the same text if and
only if they are the same ordered hierarchy of content objects.
Therefore texts are ordered hierarchies of content objects.

Other theoretical arguments are often made as well. For instance,
it is sometimes claimed that the competing non-OHCO models listed
above omit essential information about the text; that an OHCO
representation can generate the other proposed representations but not
vice versa; and that understanding and creating text essentially
involves grasping the OHCO structure of a text, but does not
essentially involve grasping any other structure -- and that each of
these facts implies that texts are OHCOs. We shall not discuss these
arguments directly here, though our counterexamples will also
apply.

The forgoing arguments provide the initial support for the
hypothesis that texts are ordered hierarchies of content objects. If
these arguments are good ones then this thesis:

explains
the success of certain representational strategies

is implied by
our theorizing about literature

matches our intuitions about what
is essential and what accidental about textual identity.

These arguments seem at least promising enough to shift the burden
of proof on to the shoulders of those who believe that the OHCO thesis
is false. Critics of this view must come up with more persuasive
alternative accounts, or, at least, counterexamples.[9]

Are there any counterexamples? In fact, there are, and in
retrospect it may seem hard to understand how these counterexamples
could have been ignored. But how they happened to be ignored or
minimized, at least by some of us, is a story that itself is an
important piece of the recent history of text encoding. It is closely
connected with the fact that the principal way in which texts were
analyzed into objects by the text processing theorists and standards
developers of the early 1980s is fundamentally different from the way
in which they are analyzed into objects by the literary and linguistic
encoding community of the late 1980s. In short: the a text as seen by
the SGML community is not the same as the text seen by the TEI
community -- that is, the accounts that they would offer of a text's
structure are significantly different.

During the initial development of descriptive markup systems and
the content object approach to text, each document was seen as having
a single natural representation as a 'logical' hierarchy of objects,
as determined by the genre of the document. What text objects might
occur in a document on this view is a function of the genre or
category of text that that document belonged to: legal contracts had
one set of objects, scientific monographs another -- poems, novels,
play scripts, letters, sermons, prayers, invoices, petitions,
receipts, summonses, and so on all had their own set of objects and
grammars that specified the syntactical relations those objects could
have. Although representations of a particular document might differ
when there was some uncertainty about the structure of the document
being represented, and the specificity or granularity of a
representation could vary, there was a sense that a single document
structure was being encoded, that the document structure was being
encoded, and any substantial differences indicated a disagreement
about the structure of the document.[10] And in any representation the objects
always seemed to form strict hierarchical structures: i.e. objects
always 'nested' and never 'overlapped' This is, indeed, the view that
is represented in the OHCO thesis.[11]

As well as the 'logical' structure of a document there were also
alternative 'physical' representations. These were typically created
by formatting or in some other way processing the logical
document. Although objects within the logical structure never
overlapped with each other, and objects from each physical structures
did not overlap with each other, it was possible for objects from
within the logical structure to overlap with objects from a physical
structure. For example, while logical objects such as sentences,
paragraphs and sections do not overlap with each other and physical
objects such as typographical lines, columns, and pages do not overlap
with each other (in a single layout design), the objects from a
logical structure frequently overlap with objects from the physical
structure: a sentence, for instance, may begin in the middle of one
typographical line and end in the middle of a later typographical
line. The SGML standard and its associated exegetical literature
reflect this view. For instance, the definition of 'document type'
indicates the role of genre in driving the hierarchical structuring of
a document instance: '4.102 document type: A class of documents
having similar characteristics; for example, journal article,
technical manual, or memo.'

Document types in SGML are given a specific document type
definition that, among other things, constrains all instances of that
type to be hierarchical structures of text objects
('elements'). Consistent with this view research projects on text
processing designed text processing systems that maintained exactly
two hierarchies, the hierarchy of logical objects and a hierarchy of
intended layout objects.(Chamberlin et al.,
1987).

When researchers from the literary and linguistic communities began
using SGML in their work, the tendency of SGML to assume that
documents could be represented as a single logical hierarchical
structure quickly created real practical problems for text encoding
projects. These problems were compellingly described by Barnard and
others in a 1987 article (Barnard et al. 1987).

Briefly the difficulty is that while the SGML world seemed to
assume that text encoders would always represent a text as a single
logical structure, there in fact turned out to be many hierarchical
structures that also had reasonable claims to being 'logical'. The
hierarchy which was taken to be the logical hierarchy of a document
was what one might call the 'editorial' hierarchy and corresponded
more or less to the 'parts of a book' (or analogues for other document
types) that one found discussed in style manuals -- objects such as
chapters, sections, paragraphs, etc. This was not surprising. SGML had
its origins in organizations concerned with using computers to create
and typeset technical documentation and other commercial
publications. In this milieu the editorial structure of a text can
easily be taken as its only logical structure.

What Barnard's article pointed out was that there are many features
of interest to scholars which taken together do not form a single
hierarchy, but which nevertheless all seem plausibly
'logical'. Consider a verse drama for instance. It contains dialogue
lines (speeches), metrical lines, and sentences. But object such as
these do fit in a single hierarchy of non-overlapping objects:
sentences and metrical lines obviously overlap (enjambment) and when a
character finishes another character's sentence or metrical line then
dialogue lines overlap with sentences and metrical lines. Yet all of
these objects have equal claim to be 'logical', at least in given our
so far very casual notion of what is meant by 'logical' -- they
certainly cannot be assigned to 'physical' hierarchies.

On the old view text objects were grouped into families as
determined by genre or category of text element (SGML 'document
type'). On the new view families are determined by the analytical or
methodological perspective on the text.

Some examples of such perspectives and typical elements they might
contain are:

Any of these structures has a plausible claim to be the 'logical
structure of the text -- for instance they all fit the notion of
'content object' both as suggested by the gloss 'having to do with
meaning and communicative intention' and as contextually defined by
the arguments given above in support of OHCO-1. But because there is
no single logical hierarchy which contains all of these structures we
can no longer claim that 'text is an ordered hierarchy of content
objects'. Once the class of logical elements in a given text is
expanded to include all of the different perspectives we will
inevitably be beset by overlapping objects: there is no unique
hierarchy of content objects which is the text. OHCO-1 is false.

Although the original OHCO thesis can be seen to be false, a weaker
revision suggests itself almost immediately and seems, moreover, to
also reflect actual encoding practice. Text encoders dealing with
overlapping objects found that although objects from different
analytical perspectives would overlap with each other, pairs of
objects from within a single analytical perspective seemed never to
overlap. For instance, in the present example prosodic objects
(stanzas, lines, half lines, couplets, etc.) do not overlap with each
other, nor do the linguistic objects (sentences, phrases, words), nor
do dramatic/editorial objects (title, cast list, acts, scenes, stage
directions, dialogue). Each perspective on the text -- prosodic,
linguistic, dramatic -- seems to determine an exact hierarchy. So
although there apparently is no single OHCO which is 'the text
itself', apart from a reference to a methodological community or
analytical perspective, the objects that are determined by these
various analytical perspectives seem to organize themselves, without
exception, into hierarchies. This was good news for text encoders
because it meant that each perspective could be represented as a
document type and was thus amenable to description within the powerful
SGML formalism -- only now document types would correspond to
analytical perspectives and not to genre. Moreover, SGML contains a
feature, CONCUR, that allows multiple hierarchies of a document to be
represented and coordinated, so it seemed that ultimately the problem
of overlapping objects would not be a practical problem for encoding
projects.

These considerations suggest a plausible revision of the OHCO
thesis: OHCO-2 An analytical perspective on a text determines an
ordered hierarchy of content objects.

A rough explication of the technical phrase 'analytical
perspective': An analytical perspective is natural family of
methodology, theory, and analytical practice

OHCO-2 reflects the commonplace truth that there is no univocal
sense of 'text', 'book', or 'document' and that consequently these
words do not, without further qualification, designate genuine
'natural kinds' that play useful roles in explanations and
descriptions of the world. Instead, they have many different senses
that play various very diverse theoretical roles and invoke different
complexes of associated concepts.

OHCO-2 does seem to reflect actual text encoding practices. When it
is discovered that an analysis of a text appears to have two objects
overlapping, encoders will typically consider this prima facie
evidence that these two objects are not things of the same sort, that
they belong to different analytical perspectives and therefore should
not be placed in the same document type. For instance, if sentences
overlap with metrical lines that is because one is a linguistic object
and one a prosodic object. If speeches overlap with pages that is
because one is a dialogue object and the other a typographical
object. On this view if two objects are both, say, truly prosodic then
they simply cannot overlap. If text encoders find that their analysis
has overlapping objects, then they typically attempt to classify one
of these objects as an object in a different analytical
perspective. That classification is generally made initially by
appealing to one's general intuitive sense of what sort of object it
is -- metrical lines, feet, couplets, all seem to belong together, as
do speeches, sentences, phrases, and words. But if the object could in
some circumstances overlap with those already considered exemplary
members of its new classification, then that is taken as evidence that
the proposed re-classification is not the right one. Objects thus
tend to sort themselves into natural families which, because there is
no overlap within a family, may be handled nicely with the apparatus
of SGML: different document types are assigned to each family and
coordinated, when a single text is involved, with CONCUR.

The principle being followed here is a logical consequence of
OHCO-2. OHCO-2.1 If two objects x and y overlap then they belong to
different perspectives

Because it generalizes actual encoding practice and seems to have
some independent plausibility, apart from its being a corollary of the
stronger and more theoretically ambitious OHCO-2, we might ask
directly about the logical status of this principle: Are texts, vis a
vis some perspective, themselves hierarchical or is it an a priori
truth of human experience that our analytical perspectives carve the
world up into hierarchies? Or perhaps hierarchical division is merely
often useful and consequently common, but not required by either the
structure of texts or the nature of human reasoning. Cynics will
suggest that text encoders had ample secondary motivation for adopting
OHCO-2.1: if perspectives did not sort themselves out into
hierarchies, then encoding projects would be deprived of the
considerable benefits of SGML formalisms.

Does every perspective determine a hierarchy of content objects?
Obviously there is a difficulty here in our rather rough understanding
of what a 'perspective' is. If 'literary studies' is itself a
perspective then indeed not all perspectives determine hierarchies:
literary studies discusses sentences, themes, pages, metrical lines --
and these, as we have seen, can overlap. We might be tempted to refine
our notion of analytical perspective in such a way as to exclude
'literary studies' as being a true perspective, perhaps because it
does not have sufficient theoretical coherence or specificity,
although such a maneuver would be suspiciously ad hoc.

There is however a quicker way of casting doubt upon
OHCO-2. Discussions of many sorts about texts are filled with
characterizations, descriptions, and hypotheses that explicitly relate
text objects from different perspectives -- chapters and themes,
speaker and meter, narrative and paragraphing. Moreover there are even
technical terms, such as enjambment and caesura, that specifically
refer to relationships between objects from overlapping
families. Because a technical vocabulary can be plausibly considered a
sign of an analytical perspective the existence of this terminology
suggests that there are analytical perspectives that contain
overlapping objects.

The final repair may be too nice for some, but having defended
versions of the OHCO thesis this far, and having found the OHCO
approach both theoretically compelling and useful as a practical
principle of encoding, we cannot resist a final, and, we think,
natural, revision. Moreover, it is one that, like the others, seems to
underly coding decisions and preferences as we have seen them made in
text projects.

First a new piece of terminology:

Sub-Perspective: x is a sub-perspective of y if and
only if x is a perspective and y is a perspective and the rules,
theories, methods, and practices of x are all included in the rules,
theories, methods, and practices of y, but not vice versa.

The idea is roughly that of a sub-discipline or some other sort of
unified and coherent part of an analytical perspective. For instance,
literary history, literary criticism, and textual criticism might be
considered 'parts of, 'areas of', or 'sub-fields of' literary
studies. And each of these in turn also has sub-fields. Textual
criticism, for instance, might be plausibly said to have as parts:
transcription, recension, and emendation. This notion of a part or
sub-field of a discipline or analytical practice is what is meant here
by 'sub-perspective'.

A version of the OHCO thesis that allows perspectives with
overlapping objects, but still asserts a significant role for
hierarchies in our understanding of what a text is:

OHCO-3: For every distinct pair of objects x and y that
overlap in the structure determined by some perspective P(1), there
exists diverse perspectives P(2) and P(3) such that P(2) and P(3) are
sub-perspectives of P(1) and x is a object in P(2) and not in P(3) and
y is an object in P(3) and not in P(2).

(or: objects may overlap in a perspective, but if they do then they
belong to different sub-perspectives of that
perspective)

The simple model of text -- an ordered hierarchy of content objects
-- had a nice platonic shape to it. The current one is like something
out of Yeatsean neo-platonism: a text now seems to be a kind of system
of concurrent perspectives which decompose into concurrent
sub-perspectives which in turn can be decomposed ... and so on, the
process perhaps continuing until atomic perspectives (foundational
analytic practices?) are reached. On this view some perspectives may
contain overlapping objects, but that is always a sign that the
perspectives are not atomic and may be decomposed further.

Unfortunately even OHCO-3, the weakest version of the OHCO thesis
(being the weakest constraint it allows the most varied and baroque
text structures) does not seem immune from counterexample. The
following have been proposed as examples of objects which can overlap
with themselves -- and so cannot plausibly be teased into different
analytical sub-perspectives.

And as well as overlapping objects there are discontiguous objects,
which are also non-hierarchical. Examples are:

Lists broken
across paragraphs

Songs or choral odes broken across other text

In some of these cases there may be ways to defend OHCO-3 and
maintain that in fact there is a stable hierarchical structure that is
being misunderstood. For instance, any apparent case of overlapping
instances of the same object can of course be challenged by proposing
a more fine-grained classification scheme. However we suspect that in
most cases it will be immediately evident that the granularity
necessary to distinguish such objects, so that they can be assigned to
different perspectives, will not plausibly correspond to alternative
analytical perspectives, but rather only to a distinctions that are
present within the text as seen from a particular analytical
perspective. For variety we illustrate this with a non-textual
example: tonal objects such as keys can overlap in modulatory
passages, sharing notes or chords -- but as there is not, within music
theory, a separate analytical perspective for every key, one
consequently cannot plausibly avoid this overlap by assigning such
objects to different perspectives (and therefore different
hierarchies).

The difficulty and subtly of these defenses suggest that may be
time to reexamine our initial provisional concern to defend
hierarchy. We have retreated from saying that texts are hierarchical,
to saying that perspectives are hierarchical, to saying that
perspectives can be decomposed into hierarchical
sub-perspectives. There are indeed enormous advantages to be had if we
can approach our subject matter in hierarchical units, but these
advantages, and even the fact that hierarchies seem prevalent and
important, should not deter us from allowing at least as many things
into our theories of text encoding as there are in the world.[13]

Even under OHCO-3 situations arise which violate simple
hierarchical notions. A number of strategies are used to represent
such cases with standard SGML techniques, but none of these is
completely satisfactory (Barnard, et al. 1988).

The most radical is simply to pick a single hierarchy as the 'real'
document hierarchy, and flatten all other hierarchies. This is
accomplished by a variety of methods generally involving the use of
zero-width tags (NULL-content tags in SGML terminology). Page numbers,
canonical reference schemes and similar sequences of objects that
cover an entire document are often represented as 'milestone' tag. The
TEI defines milestones as point labels that give a page number, or
other reference information. If the flattened hierarchy is more
complex some extra information must be implied by the zero-width
tags. For example, a text-user, or processing software, might have to
know that a 'chapter' milestone terminates any outstanding 'section'
milestones. However because strictly speaking these elements have no
scope or content the SGML mechanisms for indicating such syntactical
relations cannot be employed.

Less violent to the objects represented is the use of CONCUR. This
feature of SGML has, unfortunately, rarely been implemented, but does
allow for several parallel hierarchical decompositions of a text. It
also tends to create somewhat cumbersome and verbose markup. When
actually tagging texts, however, CONCUR seems not to represent the
text structure faithfully, despite its apparent descriptive
adequacy. CONCUR-style markup requires that each hierarchy contain the
entire document. Some hierarchies do not seem to stand on their own --
for instance, a text with metrical markup and no other tags would not
be generally useful; it might even be considered incoherent as a
representation. But CONCUR implies that such breakdowns are useful, by
requiring each set of overlapping items to be represented as a
complete hierarchy. These inadequacies are not surprising as CONCUR
was not designed to enable the representation of multiple logical
views. It was designed specifically to allow the results of
formatting to be coordinated and represented in the same file as the
source document.

The notion of multiple 'logical' views is generally absent from
SGML. Its awkwardness in coordinating multiple hierarchies is such
that Goldfarb himself has stated: 'I therefore recommend that CONCUR
not be used to create multiple logical views of a document, such as
verse-oriented and speech-oriented views of poetry' (Goldfarb, 1990, p. 304).

Finally, some non-hierarchical structures can be represented using
the tag structure known as a 'span' in the TEI. Spans are zero-width
tags that delimit the starts and ends of non-hierarchical
structures. The start and end tags are linked to each other by
explicit cross references. Given this technique, spans are even
capable of handling the multiple-strikeout case mentioned above, as
well as being the only structure that can represent hypertext links in
their full generality. The qualitative analysis community has been
using spans as the only form of markup for computer-aided ethnographic
and anthropological analyses -- providing further support for the
contention that hierarchies, while common and useful, are not inherent
to all perspectives (Miles and Huberman
1984).

The foregoing analysis seems fundamentally sound in that analytical
perspectives do seem to exist and do seem to provide fundamental
insights into the nature of texts and the methodology of text
encoding. And although we have retreated from the simple OHCO thesis,
we note that the spirit of the OHCO hypotheses is borne out to the
extent that texts qua intellectual objects still seem to be composed
of structures of meaning-related features and that, moreover, these
structures are often hierarchical.[14]

So we have the following positive conclusions:

Perspectives -- theories, methodologies, and analytical practices
-- are at least as important as genre in the identification of text
objects [15]

Perspectives frequently determine hierarchies of objects

Non-hierarchical perspectives can often be decomposed into
hierarchical sub-perspectives

Note 1 Our thinking on the topics in
this essay owes much to conversations and collaborations, spanning
many years, with Geoffrey Bilder, Lou Burnard, James H. Coombs, Steven
J. DeRose, Claus Huitfeldt, W. Richard Ristow, Michael
Sperberg-McQueen, and the members of CHUG, the Brown University
Computing in the Humanities Users' Group. It also, like so much
similar work being done today, owes an enormous debt to the Text
Encoding Initiative, and the TEI's sponsoring and funding
organizations -- in the course of pursuing its principal goal of
making machine-readable texts more useful and influential the TEI has
along the way created a wonderfully rich and exciting environment for
thinking about technology, text, and the humanities. [Back to text]

Note 2 Among the encoding projects to
which we are are particularly indebted for empirical insights into the
methodology of encoding are the Perseus Project, the Electronic Peirce
Consortium, the Bergen Wittgenstein Archives, and the Brown Women
Writers Project. In what follows we assume a basic familiarity with
text encoding and, more specifically, some understanding of SGML and
the TEI Guidlines (TEI 1990). [Back to text]

Note 3 Sperberg-McQueens's other two
axioms also help put the controversy of the 'interpretative' nature of
markup into perpective: Axiom 2: 'One's understanding of text is worth
sharing'. Axiom 3: 'No finite markup language can be complete' (Sperberg-McQueen 1991). This paper is a notable
exception to the lack of theoretical work on the methodology of text
encoding. [Back to text]

Note 4 In the terminology of graph
theory ordered hierarchies are 'ordered, rooted trees'. In linguistic
theory the ancestral and ordering relations are often separately
described as 'dominance' relations and 'precedence' relations. [Back to text]

Note 5 Elsewhere one will find
'editorial', 'logical' and 'sense' used to mean more or less the same
thing we mean here by 'content'. Words used in place of 'object' by
other authers include 'part', 'component', , and 'element'. 'Element'
is in fact the technical SGML term that corresponds to our use of
'object' -- however we continue to use the word 'object' as name for a
pre-theoretical notion that may or may not be adequately captured in
the technical vocabulary of SGML. [Back to
text]

Note 7 The classic presentation of the
view that our ontological committments, whether metaphysical or
scientific, are to be determined by examining the denoting phrases of
the relevant theoretical statements is in Willard van Orman Quine's,
'On What There Is' (Quine 1953). 'To be' quips
Quine, 'is to be the value of a bound variable'. In one form or
another this criterion for 'ontological committment' has been adopted
by many philosophers of science. [Back to
text]

Note 8 Obviously a thorough discussion
of this argument will require distinguishing and relating a variety of
objects: work and edition, type and token, etc. But the crude
presentation given here should be adequate to suggest the intuitions
behind the argument from variation. [Back to
text]

Note 9 There is a third alternative of
course: one might claim that the project -- saying 'what text is' --
is somehow muddled or incoherent, an improper question of some
sort. [Back to text]

Note 10 This view does not imply that
these structures are, or are not, "absolute" or "objective" in any
significant sense philosophical sense. [Back
to text]

Note 11 Two objects, A and B, overlap
when neither of the objects contains all of the contents of the other
object. [Back to text]

Note 12 In a talk at the Brown
University Computing in the Humanities Users Group in January 1991,
Claus Huitfeldt, Director of the Bergen Wittgenstein Project, stopped
at one point in his presentation and wrote three words on the
board. He drew a strike-out line through the first and second words,
and then a second strike-out line through the second and third
words. The text encoders present sighed -- this was a vivid example of
the vulnerability of the OHCO view of text. [Back to text]

Note 13 Initially we could dismiss
cases where, for instance, sentences might break across paragraphs or
chapters (as they might in some sort of avant garde writing) as being
too cooked-up to be considered. Now, in light of the above examples,
they seem only one more piece of evidence that the relevant logical
structures of a text are not without exception hierarchical. Yet we
note that the force and effect of such a device comes from its being
an anomaly in what otherwise tends to be a hierarchical structure. In
fact, the vivid effect of the cross-perspective overlaps cited earlier
(metrical, dramatic, linguistic) seems to owe much to the way they
work against the tendency of the logical elements of text to arrange
themselves in hierarchies. [Back to
text]

Note 14 The existence and importance of
non-hierarchical text-descriptions have been noted by Paul Rohr, in an
as yet unpublished paper (Rohr 1991). Rohr,
starting without the hierarchical bias imparted by traditional text
encoding schemes, and basing his work on deconstruction and modern
literary theory, proposes a completely non-hierarchical notion of
textual markup. [Back to text]

Note 15 In fact, the genre-based
analysis of a text is probably best treated as a special case of
analysis from an analytical perspective. [Back to text]